Instead of just rising health and damage output of monsters on advance/elite difficulty how about making them have better AI.

Normal difficulty: Monsters have normal hp and damage output.Their attack patterns are super predictable. They have very bad path finding AI and often ignore walls/get stuck on corners. They have fewer attacks and strategies.

Advanced difficulty: Monsters have slightly increased hp and damage output.Their attack patterns are more random/unpredictable. They will path find around all obstacles (just take algorithm from minecraft https://www.youtube.com/watch?v=htBo75pHW7Q) They have more attacks and strategies.

Elite difficulty: Monsters have massively increased hp and damage output. Their attack patterns are more random/unpredictable.They have insanely good pathfinding AI, and will detect/follow a player from across the map, teleporting when trapped by players or stuck. They have a hive mind and can learn from past mistakes, copying actions/attack patterns of other monsters that have survived the longest or dealt the most damage (evolving to be better like the cars in http://boxcar2d.com/).